A First Course in String Theory
14.3 Massive level in the open superstring.
What is a zero mode?
p.315 “Being zero modes, these creation operators do not contribute to the mass-squared of the states.”
How come there are creation operators that do not contribute to the mass-squared of the states?
Before each creation operator, there is a multiple which is the same as the absolute value of the index of the creation operators.
If an index can be zero, the corresponding term can be zero.
— Me@2015.09.26 08:44 PM
Consider the NS-sector:
For the NS sector, the values in are half-integers, thus cannot be zero. So every creation operator contributes to the mass-squared.
(p.312 “… the negatively moded coefficients , , , …, are creation operators, …”)
Consider the R-sector:
For the R sector, the values in are integers, thus can be zero. So some of the creation operators are zero modes.
p.315 “… the eight fermionic zero modes …”
— Me@2015-10-11 11:01:44 AM
2015.10.11 Sunday (c) All rights reserved by ACHK